Array substrate and method of fabricating the same

ABSTRACT

A method of fabricating an array substrate and a display device including the array substrate are discussed. According to an embodiment, the method includes forming a gate electrode on a substrate, forming a gate insulating layer on the gate electrode, forming an oxide semiconductor layer and an etch prevention layer on the gate insulating layer using a single mask, forming source and drain electrodes on the etch prevention layer, and forming a passivation layer including a contact hole on the source and drain electrodes and on the gate insulating layer, and forming a pixel electrode on the passivation layer and through the contact hole.

This application claims the priority benefit of Korean PatentApplication No. 10-2010-0050457, filed on May 28, 2010, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an array substrate, and moreparticularly, to an array substrate including a thin film transistorwith an oxide semiconductor layer and a method of fabricating the same.

2. Discussion of the Related Art

With rapid development of information technologies, display devices fordisplaying a large amount of information have been promptly developed.More particularly, flat panel display (FPD) devices having a thinprofile, light weight and low power consumption such as organicelectroluminescent display (OLED) devices and liquid crystal display(LCD) devices have been actively pursued and are replacing the cathoderay tubes (CRTs).

Among the liquid crystal display devices, active matrix type liquidcrystal display devices, which include thin film transistors to controlon/off the respective pixels, have been widely used because of theirhigh resolution, color rendering capability and superiority indisplaying moving images.

In addition, organic electroluminescent display devices have beenrecently spotlighted because they have many merits as follows: theorganic electroluminescent display devices have high brightness and lowdriving voltages; because they are self-luminous, the organicelectroluminescent display devices have excellent contrast ratios andultra thin thicknesses; the organic electroluminescent display deviceshave a response time of several micro seconds, and there are advantagesin displaying moving images; the organic electroluminescent displaydevices have wide viewing angles and are stable under low temperatures;since the organic electroluminescent display devices are driven by a lowvoltage of direct current (DC) 5V to 15V, it is easy to design andmanufacture driving circuits; and the manufacturing processes of theorganic electroluminescent display device are simple since onlydeposition and encapsulation steps are required. In the organicelectroluminescent display devices, active matrix type display devicesalso have been widely used because of their low power consumption, highdefinition and large-sized possibility.

Each of the active matrix type liquid crystal display devices and theactive matrix type organic electroluminescent display devices includesan array substrate having thin film transistors as switching elements tocontrol on/off their respective pixels.

FIG. 1 is a cross-sectional view of illustrating an array substrate fora liquid crystal display device or for an organic electroluminescentdisplay device according to the related art. FIG. 1 shows across-sectional view of a pixel region including a thin film transistorin the array substrate.

In FIG. 1, gate lines (not shown) and data lines 33 are formed on asubstrate 11 and cross each other to define pixel regions P. A gateelectrode 15 is formed at a switching region TrA of each pixel region P.A gate insulating layer 18 is formed on the gate electrode 15, and asemiconductor layer 28, which includes an active layer 22 of intrinsicamorphous silicon and ohmic contact layers 26 of impurity-dopedamorphous silicon, is formed on the gate insulating layer 18. Source anddrain electrodes 36 and 38 are formed on the ohmic contact layers 26.The source and drain electrodes 36 and 38 correspond to the gateelectrode 15 and are spaced apart from each other. The gate electrode15, the gate insulating layer 18, the semiconductor layer 28, and thesource and drain electrodes 36 and 38 sequentially formed at theswitching region TrA constitute a thin film transistor Tr.

A passivation layer 42 is formed on the source and drain electrodes 36and 38 and the exposed active layer 22. The passivation layer 42 has adrain contact hole 45 exposing a portion of the drain electrode 38. Apixel electrode 50 is formed independently in each pixel region P on thepassivation layer 42. The pixel electrode 50 contacts the drainelectrode 38 through the drain contact hole 45. Here, a semiconductorpattern 29 is formed under the data line 33. The semiconductor pattern29 has a double-layered structure including a first pattern 27 of thesame material as the ohmic contact layers 26 and a second pattern 23 ofthe same material as the active layer 22.

In the semiconductor layer 28 formed at the switching region TrA of therelated art array substrate, the active layer 22 of intrinsic amorphoussilicon has different thicknesses depending on the position. That is, aportion of the active layer 22 exposed by selectively removing the ohmiccontact layers 26 has a first thickness t1 and a portion of the activelayer 22 under the ohmic contact layers 26 has a second thickness t2,which is thicker than the first thickness t1. The different thicknessesof the different portions of the active layer 22 are caused by amanufacturing method, and this decreases the output characteristics ofthe thin film transistor Tr and negatively affects the performance ofthe thin film transistor Tr because the active layer 22 between thesource and drain electrodes 36 and 38, which becomes a channel of thethin film transistor Tr, has a reduced thickness.

To address this problem, a thin film transistor having an oxidesemiconductor layer of a single layer, which does not need the relatedart ohmic contact layers and which uses an oxide semiconductor materialas an active layer, has been developed.

FIG. 2 is a cross-sectional view of an array substrate including a thinfilm transistor having such an oxide semiconductor layer according tothe related art. In FIG. 2, the thin film transistor Tr is formed on asubstrate 51 and includes a gate electrode 53, source and drainelectrodes 57 and 59, and an oxide semiconductor layer 61. A gateinsulating layer 55 is disposed between the gate electrode 53 and thesource and drain electrodes 57 and 59. A passivation layer 63 covers thethin film transistor Tr and has a contact hole 65 exposing the drainelectrode 59. A pixel electrode 67 is formed on the passivation layer 63and is connected to the drain electrode 59 through the contact hole 65.

In the thin film transistor Tr of FIG. 2 having the oxide semiconductorlayer 61, ohmic contact layers are not required and are not provided,and thus the oxide semiconductor layer 61 is not exposed to etchinggases used in a dry-etching process. Therefore, lowering of the outputcharacteristics of the thin film transistor Tr is prevented orminimized.

On the other hand, since the oxide semiconductor layer 61 does not havean etch selectivity to a metal layer, the oxide semiconductor layer 61may be removed or damaged by an etchant for etching the metal layer whenthe oxide semiconductor layer 61 is exposed to the etchant. Thecharacteristics and performance of the thin film transistor may benegatively affected.

Accordingly, in FIG. 2, the thin film transistor Tr has a structure inwhich the source and drain electrodes 57 and 59 are formed, and then theoxide semiconductor layer 61 is formed on the source and drainelectrodes 57 and 59.

However, in the thin film transistor Tr having the oxide semiconductorlayer 61 on the source and drain electrodes 57 and 59, which are formedof a metallic material, there may be a problem such as poor adhesion.

In addition, as shown in the enlarged region A in FIG. 2, the oxidesemiconductor layer 61 may be disconnected or may be very thin aroundthe sides of the source and drain electrodes 57 and 59 facing each otherdue to the step profile at a region including a portion of the gateinsulating layer 55 exposed between the source and drain electrodes 57and 59, and at portions of the source and drain electrodes 57 and 59.Therefore, the thickness of the oxide semiconductor layer 61 is notuniform, and the performance characteristics of the thin film transistorTr are lowered.

In view of these limitations of the thin film transistors of FIGS. 2 and3, an etch stopper has been introduced to prevent an oxide semiconductorlayer from being exposed to an etchant. FIG. 3 is a cross-sectional viewof an array substrate including a thin film transistor having an oxidesemiconductor layer and an etch stopper according to the related art.

In FIG. 3, the thin film transistor Tr is formed on a substrate 71 andincludes a gate electrode 73, source and drain electrodes 81 and 83, andan oxide semiconductor layer 77. The thin film transistor Tr furtherincludes an etch stopper 79 on the oxide semiconductor layer 77 betweenthe source and drain electrodes 81 and 83 such that a central portion ofthe oxide semiconductor layer 77 is not exposed to an etchant when thesource and drain electrodes 81 and 83 are formed. The etch stopper 79may be formed of an inorganic insulating material.

A gate insulating layer 75 is disposed between the gate electrode 73 andthe oxide semiconductor layer 77. A passivation layer 85 covers the thinfilm transistor Tr and has a contact hole 87 exposing a portion of thedrain electrode 83. A pixel electrode 89 is formed on the passivationlayer 85 and is connected to the drain electrode 83 through the contacthole 87.

However, the array substrate of FIG. 3 including the thin filmtransistor Tr that has the oxide semiconductor layer 77 and the etchstopper 79 thereon is manufactured through a mask method composed of six(6) mask processes where one mask process is added to form the etchstopper 79. That is, there are six mask processes involved in therelated art mask method for forming the array substrate, where a firstmask process is used for forming the gate electrode, a second maskprocess is used for forming the oxide semiconductor layer, a third maskprocess is used for forming the etch stopper, a fourth mask process isused for forming the source and drain electrodes, a fifth mask processis used for forming the contact hole in the drain electrode, and a sixthmask process is used for forming the pixel electrode.

However, each of these six mask processes includes the steps of applyinga photoresist material on a layer desired to pattern, exposing thephotoresist material to light though a single photo mask, developing thelight-exposed photoresist material and thereby forming a photoresistpattern, etching the layer using the photoresist pattern, and strippingthe photoresist pattern. Thus, each mask process is complicated and manychemical solutions are used. As such, as the number of mask processes inthe mask method increases, the manufacturing time lengthens. Therefore,in the related art method and device, the productivity is lowered, moredefects are generated, and the manufacturing costs are raised.

Accordingly, in the array substrate of FIG. 3 according to the relatedart, there is a need to lower the manufacturing cost of the arraysubstrate as well as to simplify the mask method by reducing the numberof mask processes in the mask method for forming the thin filmtransistors.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an array substrateincluding an oxide semiconductor layer and a method of fabricating thesame that substantially obviate one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide an array substrateincluding an oxide semiconductor layer and a method of fabricating thesame that prevent the oxide semiconductor layer from being damaged by anetchant for patterning a metal layer and reduce the manufacturingprocesses and costs.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method offabricating an array substrate according to an embodiment includesforming a gate electrode on a substrate; forming a gate insulating layeron the gate electrode; forming an oxide semiconductor layer and an etchprevention layer on the gate insulating layer using a single mask;forming source and drain electrodes on the etch prevention layer; andforming a passivation layer including a contact hole on the source anddrain electrodes and on the gate insulating layer; and forming a pixelelectrode on the passivation layer and through the contact hole.

In another aspect, a method of fabricating an array substrate, includesforming a gate electrode on a substrate; forming a gate insulating layeron the gate electrode; forming an oxide semiconductor layer material onthe gate insulating layer; turning an upper portion of the oxidesemiconductor layer material into an etch prevention layer material;fanning a metal layer on the etch prevention layer material; forming anoxide semiconductor layer, an etch prevention layer, and source anddrain electrodes by patterning the oxide semiconductor layer material,the etch prevention layer material and the metal layer using a singlemask; forming a passivation layer including a contact hole on the sourceand drain electrodes and the gate insulating layer; and forming a pixelelectrode on the passivation layer and through the contact hole.

In another aspect, an array substrate for a display device, the arraysubstrate, includes a gate electrode formed on a substrate; a gateinsulating layer formed on the gate electrode; an oxide semiconductorlayer and an etch prevention layer fox wed on the gate insulating layer,wherein ends of the oxide semiconductor layer and ends of the etchprevention layer are aligned with each other; source and drainelectrodes formed on the etch prevention layer; a passivation layerincluding a contact hole formed on the source and drain electrodes andon the gate insulating layer; and a pixel electrode formed on thepassivation layer and through the contact hole.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view of illustrating an array substrate fora liquid crystal display device or an organic electroluminescent displaydevice according to the related art.

FIG. 2 is a cross-sectional view of an array substrate including a thinfilm transistor having an oxide semiconductor layer according to therelated art.

FIG. 3 is a cross-sectional view of an array substrate including a thinfilm transistor having an oxide semiconductor layer and an etch stopperaccording to the related art.

FIGS. 4A to 4I are cross-sectional views of illustrating a formation ofan array substrate including a thin film transistor with an oxidesemiconductor layer according to a first embodiment of the presentinvention.

FIG. 5 is a cross-sectional view of illustrating an array substrateincluding a thin film transistor with an oxide semiconductor layeraccording to another example of the first embodiment of the presentinvention.

FIGS. 6A to 6H are cross-sectional views of illustrating a formation ofan array substrate including a thin film transistor with an oxidesemiconductor layer according to a second embodiment of the presentinvention.

FIG. 7A and FIG. 7B are pictures depicting examples of thecross-sectional views of array substrates according to the related artand the present invention, respectively, after forming source and drainelectrodes of the thin film transistors.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, similar reference numbers will be used torefer to the same or similar parts.

According to the present invention, a single mask process includes thesteps of applying a photoresist material on one or more layers desiredto pattern, exposing the photoresist material to light though a singlephoto mask, developing the light-exposed photoresist material andthereby forming a photoresist pattern, etching the layer(s) using thephotoresist pattern, and stripping the photoresist pattern. As a result,in a single mask process, the layer(s) can be patterned using a singlemask.

FIGS. 4A to 4I are cross-sectional views of illustrating a formation ofan array substrate including a thin film transistor with an oxidesemiconductor layer according to a first embodiment of the presentinvention. The array substrate shown in FIGS. 4A-4I or in the subsequentfigures corresponds to an array substrate of a liquid crystal displaydevice or of an organic electroluminescent display device, but can be anarray substrate in other types of devices. The array substrate includesa plurality of thin film transistors each with an oxide semiconductorlayer according to the invention. In this regard, FIGS. 4A to 4I show apixel region including such a thin film transistor. For convenience ofexplanation, a region for the thin film transistor is defined as aswitching region TrA.

In FIG. 4A, a first metal layer is formed on a transparent insulatingsubstrate 101 by depositing a first metallic material and then ispatterned through a mask process, thereby forming a gate line and a gateelectrode 105. The gate line is formed along a first direction at aborder of a pixel region P. The gate electrode 105 extends from the gateline and is disposed at the switching region TrA. The gate line and thegate electrode 105 may have a single-layered structure or adouble-layered structure, and in FIG. 4A, the gate line and the gateelectrode 105 has a single-layered structure, for example. The substrate101 may be a glass substrate or a plastic substrate. The first metallicmaterial may be one or more selected from copper (Cu), copper alloy,aluminum (Al), aluminum alloy such as aluminum neodymium (AlNd),molybdenum (Mo) and molybdenum ally such as molybdenum titanium (MoTi).The mask process may include the steps of applying photoresist, exposingthe photoresist to light, developing the light-exposed photoresist andetching the first metal layer.

In FIG. 4B, a gate insulating layer 110 is formed on the gate line andthe gate electrode 105 by depositing an inorganic insulating material,for example, silicon oxide (SiO₂) or silicon nitride (SiN_(X)) on asubstantially entire surface of the substrate 101.

Next, in FIG. 4C, an oxide semiconductor layer material 119 is formed onthe gate insulating layer 110 by depositing an oxide semiconductormaterial, for example, indium gallium zinc oxide (IGZO) or zinc tinoxide (ZTO), by a sputtering method.

In FIG. 4D, the substrate 101 including the oxide semiconductor layermaterial 119 thereon is disposed in a vacuum chamber 195. The topsurface of the oxide semiconductor layer material 119 is treated bysupplying sulfur hexafluoride (SF₆) and oxygen (O₂) gases to the vacuumchamber 195 and generating plasma.

Here, to generate the plasma, a power supplied to the vacuum chamber 195may be 0.5 kW to 10 kW, a flow rate of sulfur hexafluoride (SF₆) may be10 sccm to 3000 sccm, a flow rate of oxygen (O₂) may be 20 sccm to 6000sccm, and a pressure of the inside of the vacuum chamber 195 may be 50mTorr to 300 mTorr. It is desirable that a mixing rate of sulfurhexafluoride (SF₆) to oxygen (O₂) may be 1:2 or 1:3.

Sulfur hexafluoride (SF₆) reacts with the oxide semiconductor layermaterial 119, and an upper portion of the oxide semiconductor layermaterial 119 is turned into an etch-prevention layer 122, whereby theetch-prevention layer 122 having a predetermined thickness is formed atthe top surface of the oxide semiconductor layer material 119 to preventthe oxide semiconductor layer material 119 from reacting with anetchant. Oxygen (O₂) prevents oxygen of the oxide semiconductor layermaterial 119, which includes oxygen therein, from coming out of theoxide semiconductor layer material 119 to thereby deterioratesemiconductor properties during the plasma treatment.

Therefore, the etch-prevention layer 122 having a certain thickness isformed at the top surface of the oxide semiconductor layer material 119by plasma-treating the oxide semiconductor layer material 119, and theoxide semiconductor layer material 119 is not affected by the etchantfor etching a metallic material due to the etch-prevention layer 122because the etch-prevention layer 122 has an increased resistantproperty to the etchant. Here, the thickness of the formedetch-prevention layer 122 may range within, e.g., 1 nm to 20 nm, andpreferably, the thickness of the etch-prevention layer 122 may rangefrom 3 nm to 9 nm. The etc-prevention layer in this and otherembodiments is a layer which is formed to prevent etching of the oxidesemiconductor layer/material when source and drain electrodes arefondled.

In FIG. 4E, the oxide semiconductor layer material 119 of FIG. 4Dincluding the etch-prevention layer 122 at the top surface is patternedthrough a mask process, and an oxide semiconductor layer 120 of anisland shape is formed at the switching region TrA. The oxidesemiconductor layer 120 corresponds to and overlaps the gate electrode105.

In the first embodiment, the oxide semiconductor layer material 119formed on a substantially entire surface of the substrate 101 is treatedby sulfur hexafluoride (SF₆) and oxygen (O₂) plasma and then ispatterned to form the oxide semiconductor layer 120. On the other hand,the plasma treatment may be performed after the oxide semiconductorlayer material 119 is patterned. FIG. 5 is a cross-sectional view ofillustrating an array substrate including such a thin film transistorwith an oxide semiconductor layer according to another example of thefirst embodiment of the present invention. As shown in FIG. 5, after theoxide semiconductor layer 120 is formed at the switching region TrA bypatterning an oxide semiconductor material layer, the plasma treatmentusing sulfur hexafluoride (SF₆) and oxygen (O₂) gases may be carriedout, and an etch-prevention layer 122 may be formed at the top surfaceof the oxide semiconductor layer 120.

Next, in FIG. 4F, a second metal layer 131 is formed on the oxidesemiconductor layer 120 by depositing one or more selected from ametallic material group including copper (Cu), copper alloy, aluminum(Al), aluminum alloy such as aluminum neodymium (AlNd), molybdenum (Mo)and molybdenum ally such as molybdenum titanium (MoTi). The second metallayer 131 may have a single-layered structure or a double-layeredstructure, and in this figure, the second metal layer 131 has asingle-layered structure, for example.

Then, photoresist is applied on the second metal layer 131, exposed tolight through a mask, and developed, thereby forming photoresistpatterns 191 on the second metal layer 131. The photoresist patterns 191correspond to areas where a data line, a source electrode and a drainelectrode are to be foamed.

In FIG. 4G, the second metal layer 131 of FIG. 4F exposed by thephotoresist patterns 191 is exposed to an etchant by using thephotoresist patterns 191 of FIG. 4F as an etching mask. Portions of thesecond metal layer 131 of FIG. 4F exposed to the etchant react with theetchant and are removed. Portions of the second metal layer 131 of FIG.4F shielded by the photoresist patterns 191 of FIG. 4F are not exposedto the etchant and remain on the substrate 101. Therefore, the secondmetal layer 131 of FIG. 4F exposed between the photoresist patterns 191of FIG. 4F at the switching region TrA are removed, and thus a centralportion of the oxide semiconductor layer 120 is exposed.

Here, the exposed central portion of the oxide semiconductor layer 120contacts the etchant for removing the second metal layer 131 of FIG. 4F.However, the oxide semiconductor layer 120 is treated by plasma ofsulfur hexafluoride (SF6) and oxygen (O2) gases, and the etch-preventionlayer 122 is formed at the top surface of the oxide semiconductor layer120. Thus, the oxide semiconductor layer 120 does not react with theetchant. Accordingly, the oxide semiconductor layer 120 is not removedat all and the inside of the oxide semiconductor layer 120 is notdamaged by the etchant.

After the etching process according to the above-mentioned steps, a dataline (not shown) and source and drain electrodes 133 and 136 are formedon the substrate 101. The data line is formed along a second directionand crosses the gate line to define the pixel region P. The source anddrain electrodes 133 and 136 are disposed at the switching region TrAand are spaced apart from each other on the oxide semiconductor layer120. The source electrode 133 is connected to the data line.

The gate electrode 105, the gate insulating layer 110, the oxidesemiconductor layer 120, and the source and drain electrodes 133 and 136constitute a thin film transistor Tr, a switching element.

The oxide semiconductor layer 120 has an ohmic contact property with themetallic material and does not require an ohmic contact layer ofimpurity-doped amorphous silicon differently from a semiconductor layerof intrinsic amorphous silicon. Therefore, the oxide semiconductor layer120 has a single-layered structure in the thin film transistor Traccording to the invention while the related art semiconductor layer hasa double-layered structure of an active layer of intrinsic amorphoussilicon and ohmic contact layers of impurity-doped amorphous silicon.

The thin film transistor Tr having the single-layered oxidesemiconductor layer 120 does not need an additional dry etching step forremoving the impurity-doped amorphous silicon layer between the sourceand drain electrodes 133 and 136 to form the ohmic contact layers afterforming the source and drain electrodes 133 and 136. Therefore, theoxide semiconductor layer 120 is not damaged by the dry etching step,and the characteristics of the thin film transistors Tr are notdeteriorated.

Then, the photoresist patterns 191 of FIG. 4F on the source and drainelectrodes 133 and 136 are stripped and removed, thereby exposing thedata line and the source and drain electrodes 133 and 136 as shown inFIG. 4G.

In FIG. 4H, a passivation layer 140 is formed on the data line and thesource and drain electrodes 133 and 136 by depositing an inorganicinsulating material such as silicon oxide (SiO₂) or silicon nitride(SiN_(X)), or applying an organic insulating material such asbenzocyclobutene (BCB) or photo acryl. In the figure, the passivationlayer 140 is formed of an organic insulating material and has an evensurface, for example. If the passivation layer 140 is formed of aninorganic material, the passivation layer 140 may have an uneven surfacedue to the steps of the layers under the passivation layer 140.

The passivation layer 140 is patterned through a mask process, therebyforming a drain contact hole 143 exposing a part of the drain electrode136 at the switching region TrA.

In FIG. 4I, a transparent conductive material layer is formed on thepassivation layer 140 having the drain contact hole 143 by depositing atransparent conductive material, for example, indium tin oxide (ITO) orindium zinc oxide (IZO) on a substantially entire surface of thestructure of FIG. 4H. The transparent conductive material layer ispatterned through a mask process, thereby fowling a pixel electrode 150in the pixel region P. The pixel electrode 150 contacts the drainelectrode 136 through the drain contact hole 143. Accordingly, the arraysubstrate according to the first embodiment of the present invention iscompleted.

As discussed above, the above-mentioned array substrate including thethin film transistor Tr having the oxide semiconductor layer 120according to the present invention is manufactured by five (5) maskprocesses: a first mask process is used for forming the gate electrode,a second mask process is used for forming the oxide semiconductor layerand the etch-prevention layer, a third mask process is used for formingthe source and drain electrodes, a fourth mask process is used forforming the contact hole in the drain electrode, and a fifth maskprocess is used for forming the pixel electrode. In the manufacturingmethod of the array substrate according to the first embodiment of thepresent invention, one mask process is omitted as compared with themanufacturing method of the related art array substrate including a thinfilm transistor having an oxide semiconductor layer and an etch stopper,which uses the six (6) mask processes. Therefore, the manufacturingprocesses are simplified, and the manufacturing costs are reduced usingthe present invention.

FIGS. 6A to 6H are cross-sectional views of illustrating a method offorming an array substrate including a thin film transistor with anoxide semiconductor layer according to a second embodiment of thepresent invention. FIGS. 6A to 6H show a pixel region including such athin film transistor. For convenience of explanation, the same parts asthe first embodiment are designated by the similar references to thefirst embodiments. Steps of forming a gate line and a gate electrode,forming a gate insulating layer, and forming an oxide semiconductormaterial layer in the second embodiment are the same as the firstembodiment, and thus for the sake of brevity, the explanations for thesesame steps will be omitted or at minimal.

In FIG. 6A, a gate electrode 205 and a gate line are formed on asubstrate 201, a gate insulating layer 210 is formed on the gateelectrode 205 and the gate line, and an oxide semiconductor materiallayer 219 is formed on the gate insulating layer 210. The substrate 201including the oxide semiconductor material layer 219 thereon is disposedin a vacuum chamber 295. The top surface of the oxide semiconductormaterial layer 219 is treated by supplying sulfur hexafluoride (SF₆) andoxygen (O₂) gases to the vacuum chamber 295 and generating plasma tothereby form am etch-prevention layer 222 having a certain desiredthickness at the top surface of the oxide semiconductor material layer219. The certain desired thickness of the etch-prevention layer 222 mayrange from, e.g., 1 nm to 20 nm, and preferably, the thickness of theformed etch-prevention layer 222 may range from 3 nm to 9 nm.

Here, the conditions for treating the top surface of the oxidesemiconductor material layer 219 may be the same as those of the firstembodiment.

Next, in FIG. 6B, a second metal layer 231 is formed on the oxidesemiconductor material layer 219 treated by the plasma of sulfurhexafluoride (SF₆) and oxygen (O₂) by depositing one or more selectedfrom a metallic material group including copper (Cu), copper alloy,aluminum (Al), aluminum alloy such as aluminum neodymium (AlNd),molybdenum (Mo) and molybdenum ally such as molybdenum titanium (MoTi).The second metal layer 231 may have a single-layered structure or adouble-layered structure, and in the figure, the second metal layer 231has a single-layered structure, for example.

Then, a photoresist layer 290 is formed on the second metal layer 231.The photoresist layer 290 is exposed to light through a mask 300, whichincludes a light-transmitting portion TA, a light-blocking portion BAand a half light-transmitting portion HTA. The half light-transmittingportion (or a semi light-transmitting portion) HTA may include slits ora multiple-coating layer to control the intensity of light passingtherethrough and may have a light transmittance larger than thelight-blocking portion BA and smaller than the light-transmittingportion TA.

Next, in FIG. 6C, the light-exposed photoresist layer 290 of FIG. 6B isdeveloped, thereby forming a first photoresist pattern 291 a and asecond photoresist pattern 291 b on the second metal layer 231. Thefirst photoresist pattern 291 a has a first thickness, and the secondphotoresist pattern 291 b has a second thickness thinner than the firstthickness. The first photoresist pattern 291 a corresponds to areaswhere a data line and source and drain electrodes at the switchingregion TrA are to be formed, and the second photoresist pattern 291 bcorresponds to an area between the source and drain electrodes at theswitching region TrA. The second photoresist pattern 291 b maycorrespond to the gate electrode 205. The portions of the photoresistlayer 290 of FIG. 6B corresponding to other areas are removed to therebyexpose the second metal layer 231.

In FIG. 6D, the second metal layer 231 of FIG. 6C exposed by the firstand second photoresist patterns 291 a and 291 b is exposed to an etchantby using the first and second photoresist patterns 291 a and 291 b as anetching mask. Portions of the second metal layer 231 of FIG. 6C exposedto the etchant react with the etchant and are removed from the substrate201 to thereby expose the oxide semiconductor material layer 219 of FIG.6C. Portions of the second metal layer 231 shielded by the first andsecond photoresist patterns 291 a and 291 b are not exposed to theetchant and remain on the substrate 201.

Next, the portions of the oxide semiconductor material layer 219 of FIG.6C that were exposed as the portions of the second metal layer 231 ofFIG. 6C were removed, are removed. As a result, portions of the gateinsulating layer 219 around the transistor area TrA are exposed.

After the above-mentioned steps, a data line, a source drain pattern 232and an oxide semiconductor layer 220 are formed on the gate insulatinglayer 210. The data line is formed along a second direction and crossesthe gate line to define the pixel region P. The source drain pattern 232is disposed at the switching region TrA and is connected to the dataline. The oxide semiconductor layer 220 is disposed under the sourcedrain pattern 232. Also, a dummy pattern of the same material as theoxide semiconductor layer 220 is formed under the data line.

In FIG. 6E, an ashing process is performed to the substrate 201including the source drain pattern 232 and the data line thereon, andthe second photoresist pattern 291 b of FIG. 6D having the secondthickness is removed, thereby exposing a central portion of the sourcedrain pattern 232 at the switching region TrA. At this time, the firstphotoresist pattern 291 a is also partially removed by the ashingprocess and remains on the source drain pattern 232 while having areduced thickness.

In FIG. 6F, the source drain pattern 232 of FIG. 6E exposed by the firstphotoresist pattern 291 a is exposed to an etchant, and the centralportion of the source drain pattern 232 of FIG. 6E corresponding to thegate electrode 205 is removed, thereby forming source and drainelectrodes 233 and 236 and exposing a portion of the oxide semiconductorlayer 220 between the source and drain electrodes 233 and 236. Here, theexposed portion of the oxide semiconductor layer 220 contacts theetchant for removing the source drain pattern 232 of FIG. 6E. However,the oxide semiconductor material layer 210 of FIG. 6A is treated byplasma of sulfur hexafluoride (SF₆) and oxygen (O₂) gases, and theetch-prevention layer 222 of a predetermined thickness is formed at thetop surface of the oxide semiconductor layer 220. Thus, the oxidesemiconductor layer 220 does not react with the etchant. Accordingly,the oxide semiconductor layer 220 is not removed and the inside of theoxide semiconductor layer 220 is not damaged by the etchant. Thethickness of the etch-prevention layer 222 may range from, e.g., 1 nm to20 nm, and preferably, the thickness of the etch-prevention layer 222may range from 3 nm to 9 nm.

The gate electrode 205, the gate insulating layer 210, the oxidesemiconductor layer 220, and the source and drain electrodes 233 and 236constitute a thin film transistor Tr, a switching element.

In FIG. 6G, the first photoresist pattern 291 a of FIG. 6F on the dataline and the source and drain electrodes 233 and 236 are stripped andremoved, thereby exposing the data line and the source and drainelectrodes 233 and 236.

In FIG. 6H, a passivation layer 240 is formed on the data line and thesource and drain electrodes 233 and 236 by depositing an inorganicinsulating material such as silicon oxide (SiO₂) or silicon nitride(SiN_(X)), or applying an organic insulating material such asbenzocyclobutene (BCB) or photo acryl. In the figure, the passivationlayer 240 is formed of an organic insulating material and has an evensurface, for example. If the passivation layer 240 is formed of aninorganic material, the passivation layer 240 may have an uneven surfacedue to the steps of the layers under the passivation layer 240.

The passivation layer 240 is patterned through a mask process, therebyforming a drain contact hole 243 exposing a part of the drain electrode236 at the switching region TrA.

Next, a transparent conductive material layer is formed on thepassivation layer 240 having the drain contact hole 243 by depositing atransparent conductive material, for example, indium tin oxide (ITO) orindium zinc oxide (IZO) on a substantially entire surface of thestructure including the substrate 201. The transparent conductivematerial layer is patterned through a mask process, thereby forming apixel electrode 250 in the pixel region P. The pixel electrode 250contacts the drain electrode 236 through the drain contact hole 243.Accordingly, the array substrate according to the second embodiment ofthe present invention is completed.

The above-mentioned array substrate according to the second embodimentis manufactured by using four (4) mask processes: a first mask processis used for forming the gate electrode, a second mask process is usedfor forming the oxide semiconductor layer, the etch-prevention layer,and the source and drain electrodes, a third mask process is used forforming the contact hole in the drain electrode, and a fourth maskprocess for forming the pixel electrode. In the manufacturing method ofthe array substrate according to the second embodiment, two maskprocesses are omitted as compared with the manufacturing method of therelated art array substrate including a thin film transistor having anoxide semiconductor layer and an etch stopper where the six maskprocesses are used. Therefore, the manufacturing processes aresimplified, and the manufacturing costs are reduced according to thepresent invention. Moreover, the oxide semiconductor material layer istreated by sulfur hexafluoride (SF₆) and oxygen (O₂) plasma, and even ifthe oxide semiconductor layer is exposed to the etchant for etching themetal material, the oxide semiconductor layer does not react with theetchant and is not damaged.

FIG. 7A is a picture of a cross-sectional view of an array substrateafter the source and drain electrodes are formed according to therelated art, and FIG. 7B are pictures of a cross-sectional view of anarray substrates having the thin film transistor according to thepresent invention.

In FIG. 7A, the oxide semiconductor layer is not treated by sulfurhexafluoride (SF₆) and oxygen (O₂) plasma. The oxide semiconductor layeris exposed to the etchant for forming the source and drain electrodesand is removed. Thus, the oxide semiconductor layer hardly remains atthe switching region.

On the other hand, in FIG. 7B, the oxide semiconductor layer, moreparticularly, the oxide semiconductor material layer is treated bysulfur hexafluoride (SF₆) and oxygen (O₂) plasma. Thus even though theoxide semiconductor layer is exposed to the etchant for forming thesource and drain electrodes, the oxide semiconductor layer is notremoved.

In the present invention, the surface of the oxide semiconductor layeris treated by plasma, and thus the oxide semiconductor layer does notreact with an etchant for removing a metallic material. Therefore, theoxide semiconductor layer is not damaged by the etchant, and thecharacteristics of the thin film transistor are not deteriorated.

Furthermore, an etch stopper, which prevents the oxide semiconductorlayer from being exposed to the etchant, can be omitted due to theplasma treatment, and in the manufacturing method of an array substrateaccording to the present invention, one or two mask processes can beeliminated as compared with the manufacturing method of an arraysubstrate according to the related art. Accordingly, the manufacturingprocesses can be simplified, and the manufacturing costs are decreasedaccording to the present invention.

The array substrate according to the present invention can be used forflat panel display (FPD) devices such as organic electroluminescentdisplay (OLED) devices, liquid crystal display (LCD) devices andelectrophoretic display (EPD) devices.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of fabricating an array substrate,comprising: forming a gate electrode on a substrate; forming a gateinsulating layer on the gate electrode; forming an oxide semiconductorlayer and an etch prevention layer on the gate insulating layer using asingle mask; forming source and drain electrodes on the etch preventionlayer; and forming a passivation layer including a contact hole on thesource and drain electrodes and on the gate insulating layer; andforming a pixel electrode on the passivation layer and through thecontact hole.
 2. The method according to claim 1, wherein the step offorming the oxide semiconductor layer and the etch prevention layerincludes: forming an oxide semiconductor layer material on the gateinsulating layer; turning an upper portion of the oxide semiconductorlayer material into an etch prevention material layer; and patterningthe oxide semiconductor layer material and the etch prevention materiallayer using the single mask to form the oxide semiconductor layer andthe etch prevention layer.
 3. The method according to claim 2, whereinthe turning step includes applying a plasma treatment on the oxidesemiconductor layer material.
 4. The method according to claim 3,wherein the plasma treatment involves applying a sulfur hexafluoride(SF₆) and oxygen (O₂) plasma.
 5. The method according to claim 1,wherein the step of forming the oxide semiconductor layer and the etchprevention layer includes: forming the oxide semiconductor layer on thegate insulating layer using the single mask; and turning an upperportion of the oxide semiconductor layer into the etch prevention layer.6. The method according to claim 5, wherein the turning step includesapplying a plasma treatment on the oxide semiconductor layer.
 7. Themethod according to claim 6, wherein the plasma treatment involvesapplying a sulfur hexafluoride (SF₆) and oxygen (O₂) plasma.
 8. Themethod according to claim 1, wherein the steps of the method areperformed using five mask processes.
 9. The method according to claim 1,wherein the array substrate is an array substrate of a liquid crystaldisplay device or an array substrate of an organic electroluminescentdisplay device.
 10. The method according to claim 1, wherein the etchprevention layer has a thickness of approximately 1 to 20 nanometers.